Threatened Mammals With Alien Populations: Distribution, Causes, and Conservation

Many alien species are safe in their native ranges, but some are threatened. This creates a conundrum for conservation and invasion science. We analyzed the distributions, introduction pathways, threats, and conservation strategies of threatened mammals with alien populations globally. We reassessed their hypothetical IUCN Red List category including the alien part of the range. Among 230 alien mammals, 36 are threatened in their native range, either critically endangered (17%), endangered (25%), or vulnerable (58%). These species were mainly introduced for hunting and exchanged within Asia, with introduced ranges concentrated in south-eastern Asia and eastern Australia. They face multiple threats, particularly from biological resource use. Conservation strategies are mainly related to species management. Including alien populations in the assessments reduces extinction risk of 22% of the species. Although some of these alien populations may have conservation value, conservation managers should carefully consider them on a case-by-case basis to avoid negative impacts on biodiversity.